Some gas-powered tools with spark-ignitions have two part combustion chambers: a pre-combustion chamber and a main combustion chamber. Ignition originates in the pre-combustion chamber. Some unburned fuel and air in the pre-combustion chamber is forced ahead of a flame jet into the main combustion chamber. Upon arrival, the flame jet triggers combustion of a compressed fuel and air mixture in the main combustion chamber. The detonation (combustion) in the main combustion chamber drives a piston or performs other useful work, such as launching a projectile.
When a combustion cycle is initiated, both the pre-combustion chamber and the main combustion chamber are charged with a mixture of fuel and air, and the pre-established mixture within the pre-combustion chamber is then ignited. Ideally, a generated flame front propagates through the pre-combustion chamber so as to push unburned fuel and air in front of it toward the main combustion chamber, thereby further mixing and compressing the fuel and air in the main combustion chamber. In some designs, a check valve regulates flows between the pre-combustion chamber and the main combustion chamber so as to permit the unburned fuel and air and the flame front to enter the main combustion chamber from the pre-combustion chamber but to limit any reverse flow of combustion products from the main combustion chamber back into the pre-combustion chamber. As the flame front enters the main combustion chamber, it ignites the compressed fuel and air mixture disposed within the main combustion chamber. Elevated combustion pressure within the main combustion chamber leads to a more efficient combustion within the main combustion chamber, and such elevated pressures can more effectively and powerfully perform useful work, such as driving of fasteners with combustion-powered fastener-driving tools.
Generally, for purposes of (a) recharging the pre-combustion and main combustion chambers with mixtures of fuel and air and (b) discharging exhaust gases from the combustion chambers, a bypass passageway controlled by a bypass valve interconnects the pre-combustion and main combustion chambers. During recharging, the fuel air mixture enters the pre-combustion chamber through an intake valve and reaches the main combustion chamber through the bypass passageway. During discharging, exhaust gases in the pre-combustion chamber enter the main combustion chamber through the bypass passageway and exit the main combustion chamber through an exhaust valve. The bypass valve is opened for purposes of recharging or discharging the combustion chambers, but is closed during combustion.
Other designs with two-stage combustion chambers (i.e., a pre-combustion chamber and a main combustion chamber) provide a control wall between the chambers with limited size orifices through the wall. The orifices allow flame jets to pass from the pre-combustion chamber to the main combustion chamber for detonating the fuel/air mix in the main combustion chamber while providing a wall for reflecting compression waves within the main combustion chamber in a direction for accomplishing work.
Check valves that are free-flowing in both directions at low pressure values been envisioned for controlling flows between the pre-combustion and main combustion chambers. The recharging and discharging operations take place at the relatively low pressure values at which the check valves are free flowing.
The bypass valves add to the design complexity of linear motors by requiring the opening and closing of the bypass valve in response to different stages in the combustion cycle of the motor including recharging (open), detonating (closed), and discharging (open). Limited orifices through control walls, whether regulated by check valves or not, tend to impose restrictions on the free flow of gasses between the chambers and can result in reduced charging and discharging efficiencies.